Because of his condescending attitude and his self-righteousness.
Explanation:
The character of Malvolio is from William Shakespeare's "Twelfth Night". He initially seems to be just a source of sub-plot and source of comedy for the story but as the story progresses, he becomes more of a major character.
Malvolio is a self centered character, working on his own selfish achievements and wanting nothing but power and higher social status. He vies for Lady Olivia's love, not because he loves her but mostly for the social status and power that will come with her hand in marriage. The other characters in Lady Olivia's household hate him as he has a condescending attitude and is self righteous, caring for none but himself.
